The invention relates to UHF and VHF range antenna elements for antennas radiating broadband in flight direction of an airborne vehicle with empennage parts.
Helical antennas are currently used for reconnaissance and direction finding in the VHF range because of their relatively compact construction. However, at low frequencies (<1 GHz) and with structural volumes that are as small possible, these antennas either have a much reduced antenna gain, or their dimensions are not suitable for integration in the airborne vehicle.
Thus, in airborne vehicles with a length on the order of magnitude of the wavelength employed, the problem encountered within the low frequency ranges (<1 GHz) is that directionally radiating antennas, because of their aperture requirements, can no longer be arranged within the airborne vehicle, or it is no longer possible to achieve a directional antenna behavior.
German Patent DE 195 43 321 discloses an airborne vehicle with antenna elements integrated in dielectric wing elements for communications purposes. From Funkschau 6, 1998, Antennen [Antennas], Part 10, it is further known to arrange planar antennas on dielectric ceramic substrates.
The resulting planar structures, however, (e.g., patch antennas) do not have the directional effect necessary for direction finding. Furthermore, this type of antenna used in the two cited sources cannot be arranged on the airborne vehicles available for the application such that radiation in flight direction is achieved. Even the arrangement in an array as described in the first cited source—if the required surface were available—does not change this fact because the gain is clearly reduced if the radiation is deflected from the surface normal by more than 60°.
A further reason why patch elements appear unsuitable for the application according to the invention is the required broadbandedness, which at 1:20 cannot be achieved with the described antennas. This antenna type is thus in principle unsuitable for the planned direction finding in flight direction.
Antennas with an externally similar construction are used in communications technology (e.g., aerodynamically shaped blade antennas in rail vehicles). The essential difference compared to these structures is the physical separation of radome and antenna and the fact that these antennas radiate non-directionally.
The object of the invention is to provide an antenna arrangement in which the antenna elements, despite the spatial and the mechanical limitations imposed by the airborne vehicle, exhibit the required behavior, i.e., in particular, radiate directionally broadband in flight direction.
According to the invention this object is attained by the features set forth in the characterizing part of Claim 1.
Thus, the empennage of the airborne vehicle is used to integrate antenna structures that radiate directionally broadband in flight direction without interfering with the mechanical functionality of the empennage area.